Photographic materials often contain filter dyes to absorb light from different regions of the spectrum, such as red, blue, green, ultraviolet, and infrared, to name a few. These filter dyes are often required to perform the function of absorbing light during exposure of the material so as to prevent or at least inhibit light of a region of the spectrum from reaching at least one of the radiation-sensitive layers of the element.
After processing of the element, however, the continued presence of the filter dye will adversely affect the image quality of the photographic material. It is therefore desirable to use filter dyes that will be solubilized and removed or at least decolorized during photographic processing. Dyes that are easily solubilized, however, tend to wander throughout the photographic material during coating, adversely affecting the final image quality.
To prevent dye wandering, the dyes are often coated with a mordant to bind the dye in the layer in which it is coated. Dye mordants, while often useful, tend to either bind the dye too strongly, inhibiting removal of the dye during photographic processing, or too weakly, thus not preventing dye wandering.
Lemahieu et al describe in U.S. Pat. No. 4,092,168 a combination of specific monomethine oxonol and pentamethine carboxy-substituted oxonol dyes useful as antihalation dyes. The dyes are insoluble at coating pH's, thus eliminating the need for a dye mordant, and are soluble for removal and/or decolorization at processing pH's. These dyes are disclosed as being dispersible as solid particles in aqueous hydrophilic colloid compositions; however, no suggestion is given that any other dyes might possess the same beneficial solubility properties. The reference discusses the absorbance properties of the dyes and their suitability for antihalation use, but no teaching whatsoever is presented as to what other dyes might possess the beneficial solubility properties of being aqueous-insoluble at coating pH's and highly aqueous-soluble at processing pH's. There is also no teaching that would enable anyone as to how to choose dyes other than those specifically disclosed in the U.S. Pat. No. 4,092,168 to obtain those properties.
Postle et al U.S. Pat. Nos. 4,294,916 and 4,294,917 describe solid dispersions of photographic filter dyes, including a carboxyphenyl-substituted dye as preparation 6 of the '917 patent. The dyes are said to offer the advantage of broad spectral absorption. Many of the dye dispersions described in these references, however, are subject to dye wandering in the hydrophilic layers of photographic elements. No teaching is made as to what dyes might possess the beneficial solubility properties of being aqueous-insoluble at coating pH's so as to be substantially free from dye wandering in a photographic element, yet highly aqueous-soluble at processing pH's for decolorization.
Kreuger et al describe in U.S. Pat. No. 4,420,555 specific yellow filter dyes for incorporation into film-forming polymeric binders in photographic elements. The dyes are preferably incorporated in the binders in loaded polymeric latexes. These dyes are disclosed as being removable and/or decolorizable during photographic processing. The dyes are not disclosed as being coatable as solid particle dispersions and, as with U.S. Pat. No. 4,092,168, there is no teaching or suggestion that any dyes other than those specifically disclosed (or, for that matter, even the dyes disclosed therein) might possess the beneficial concomitant advantages of being aqueous-insoluble at coating pH's and aqueous-soluble at processing pH's.
Prior to the present invention, there has been a lack of recognition in the prior art that there might exist a broad class of dyes having a specific set of properties that allow them to be prepared and incorporated into photographic compositions and elements as solid particle dispersions that are aqueous-insoluble at coating pH's and aqueous-soluble at photographic processing pH's. It would, of course, be highly desirable to provide a broad class of filter dyes for use in photographic elements that do not wander during coating, are fully solubilized during processing, and do not require a mordant.
It has now been discovered that a broad class of dyes, where the dye and its substituents are chosen so as to meet a specific combination of solubility criteria for both acid/base and nonpolar/polar systems, can be prepared as solid particle dispersions having the above-described beneficial solubility properties.